1. Field of the Invention
The present invention relates generally to an injection molding apparatus and, in particular, to an improved seal located between a manifold and a nozzle.
2. Background Art
A common problem associated with hot runner injection molding systems is the leaking of molten plastic that can occur between the manifold and the nozzle. Leaking is typically caused by operation of the hot runner injection molding system outside of the designated operating window. There are many different nozzle designs that have attempted to stop leakage from occurring.
For example, in one design, a pair of spacers located between a manifold and a cover plate or a hot runner plate, such as disclosed in U.S. Pat. Nos. 6,309,207, 6,062,846 and U.S. patent application Publication No. 2001/0011415, apply a contact pressure between the nozzle body and the manifold to achieve a seal therebetween. The spacers are arranged in series with a first spacer abutting the manifold and a second spacer abutting the cover plate. The second spacer has a different response characteristic to compressive pressures than the first spacer.
WO 01/87570 A1 (U.S. Pat. No. 6,669,462) discloses a non-flat sealing interface, which is provided between a nozzle and a manifold. A spring urges the nozzle against the manifold to produce a pressure distribution with a peak sealing pressure that occurs adjacent the nozzle and manifold melt channels. Similarly, U.S. Pat. No. 5,896,640 discloses a sealing insert that abuts a nozzle shoulder. The sealing insert generates an angular sealing force and maintains sealing contact between the nozzle and manifold channels. The sealing insert produces a peak sealing pressure that occurs adjacent the nozzle and manifold channels.
Despite the existence of previous designs, there remains a need for a manifold to nozzle seal that has improved reliability and cost effectiveness.